This project involves the study of the leukemia-colony forming cell population (L-CFC) in patients with acute myelogenous leukemia (AML). In one aspect of this study, the cell surface antigens expressed by the L-CFC will be examined in patients with AML using a panel of myeloid-specific monoclonal antibodies and complement-mediated cytotoxicity. Patients will be examined serially on subsequent relapses to determine whether the L-CFC phenotype is stable with time. The findings from these studies will then be compared to a series of experiments designed to examine the inducibility to maturation of the L-CFC using various agents known to effect myeloid cell differentiation. The agents to be tested include recombinant gamma interferon, 1,25 dihydroxyvitamin D3, and cis-retinoic acid. Changes in surface antigens, proliferative potential, and morphology will be examined in the L-CFC exposed to optimal concentrations of the maturation-inducing agents. The studies are designed to examine whether the L-CFC in AML is responsive to agents of differentiation, and to determine whether response is manifested in cellular changes similar to those of normal myelopoiesis (i.e., expression of a more differentiated cell phenotype and a reduction in cellular proliferation). Another aspect is to correlate the cell surface antigenic display of both normal and leukemic myeloid cells with oncogene expression. The expression of three myeloid-associated cellular oncogenes (c-onc) will be studied: N-ras, c-myc and c-fos. Oncogene expression will be quantified by hybridization of probes to c-onc RNA extracted from normal myeloid subpopulations (monocytes and neutrophils) and from leukemia blast cell populations from patients with AML. Expression of oncogene protein products will be determined by immunofluorescence studies using antisera to the oncogene proteins, and by immunoprecipitation studies of radiolabelled cell lysates. The aim of these studies is to correlate the expression of oncogenes with patterns of myeloid cell-surface antigens on normal and malignant cells to determine whether there is a relationship with differentiation status. Results will further our understanding of leukemia cell biology in AML, and are directed towards clarifying the maturational defect that occurs in myelogenous leukemia. By determining the maturational capabilities of the L-CFC population, alternative approaches to therapy, including immunotherapy and maturation-inducing therapy, may result.